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From André Warnier>
Subject Re: implement dynamic filter
Date Wed, 22 Jul 2009 12:36:07 GMT
lanxiazhi wrote:
> hello,
> I have a web app in tomcat ,where exists some .jsp,.vm files,
> these files are saved using different encoding(I think).when requested,some
> of them display urgly,garbled.
> so I think maybe I can implement such a filter:first read the content of the
> file,and* *decide which charset it's saved,and set the ServletResponse's
> character encoding accordingly.
> Is that possible ? If possible ,how to decide the charset quickly ,without
> slowing down the server?
> thanks
> lanxiazhi

Answering your last question first : that is close to impossible.
It is not even the question of slowing down the server, it is really 
that detecting the charset is not possible in a number of cases.
Very shortly :
- it is is usually possible to detect if a given file is valid UTF-8 or not.
- but it is not possible to decide if a file encoded in an 8-bit 
alphabet (such as iso-8859-1) is iso-8859-1 or iso-8859-2 or any other 
8-bit character set (because they all use bytes with a value between 
\x00 and \xFF, so how can you decide ?).

Given this, your best bet is to correct the problem at the source :
Any text file, in any original encoding, can be converted to 
UTF-8/Unicode.  So clean up the original files, and always send them 
back as UTF-8.  All reasonably recent browsers support that.

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